1. Field of the Invention
The present invention relates to a batch mixer that mixes mixing materials, particularly to a batch mixer having a constitution where a floating weight for pressing the mixing materials into a mixing chamber is elevated and lowered.
2. Description of the Prior Art
A batch mixer of this type is disclosed in U.S. Pat. No. 5,783,983, for example. Herein, the mixer is constituted that a hydraulic cylinder for lowering the floating weight to be pressed to the mixing chamber side is provided, a pneumatic/hydraulic pressure converter that converts pressure between a hydraulic pressure side and a pneumatic pressure side is provided separately from a mixer main body, and the hydraulic pressure side of the hydraulic cylinder is connected to the hydraulic pressure side of the pneumatic/hydraulic pressure converter. In this batch mixer, the mixing materials are gradually led into the mixing chamber by lowering the floating weight while a cushioning function is properly exerted on the weight by the air pressure of the pneumatic/hydraulic pressure converter, and the mixing materials can be mixed smoothly.
Further, the above-described batch mixer is provided with a direction switching solenoid valve for switching the advance/withdrawal of the hydraulic cylinder and an ON/OFF-type limit switch for monitoring the movement of the floating weight to be elevated and lowered, and is constituted that the direction switching solenoid valve is switched in response to a signal from the limit switch when the weight reaches a lower limit position to stop the lowering of the weight.
In such a batch mixer, demands for new mixing methods such that mixing is performed while a weight position is fixed on various positions and pressing pressure of the weight is arbitrarily controlled in pressing or mixing materials are increasing due to circumstances such as diversified mixing materials in recent years.
However, since the batch mixer of U.S. Pat. No. 5,783,983 detects the position of the floating weight by an ON/OFF signal from the limit switch, the position of the floating weight must be changed in order to change the weight position, and its labor was complicated.
Further, in the above-described batch mixer, the pneumatic/hydraulic pressure converter must be installed around the batch mixer, and a large installing space was required. Additionally, in the above-described batch mixer, it is theoretically possible to change the pressing pressure of the weight by changing air supply to the air pressure side of the pneumatic/hydraulic pressure converter, but a large volume of air supply/discharge is necessary if the control of changing the weight pressing pressure by a large amount, and a long time is taken in changing pressure as well, so that it was virtually impossible to perform pressure control within a predetermined mixing time.
Furthermore, although a type of mixer for lowering the floating weight by a pneumatic cylinder is conventionally known as the batch mixer, it required a large pneumatic cylinder and there was a room for improvement from the viewpoint of equipment cost and space. In addition, a large volume of air was required for elevating/lowering the weight, running cost was increased, and it was not preferable from the viewpoint of energy saving too. Moreover, because it is a positional control using air being compressed fluid, it was difficult to control the position of the weight at various positions with good accuracy, and the control of changing the weight pressing pressure by a large amount within a predetermined mixing time was also difficult similar to the above-described U.S. Pat. No. 5,783,983.